Conventionally, a technology disclosed, for example, in WO 2008/081861 has been proposed as a technology for a titanium-based or non-titanium based member having antibacterial activity in an implant.
WO 2008/081861 discloses an antibacterial member coated with titanate, including a substrate, a layer of a nanosheet, nanotube, nanofiber or nanocrystal made of a crystalline alkali titanate formed on the substrate, and a silver titanate layer in which a portion or all of an alkali component of the alkali titanate is substituted with silver ions.
WO 2008/081861 also discloses, as a method for producing the antibacterial member, the method comprising the steps of (i) subjecting a titanium-based substrate to a hydrothermal treatment in an aqueous alkali solution at a temperature of 110 to 180° C., (ii) heat-treating the product after subjecting to the hydrothermal treatment at 200 to 700° C., and (iii) washing and drying the product after subjecting to the heat treatment, and immersing the product in an aqueous silver ion-containing solution.
Since the antibacterial member disclosed in WO 2008/081861 includes the silver titanate layer, high antibacterial activity is obtained. However, there was a problem in that when this antibacterial member is used in an implant, titanate or silver titanate makes contacted with living tissues, resulting in poor compatibility between the implant and living tissues.
In the silver titanate layer of the antibacterial member, since a portion or all of the alkali component of the alkali titanate is substituted with silver ions, the degree of elution of silver ions varies drastically depending on a usage state of an implantation site, as described in Example 10. Therefore, this antibacterial member may not exhibit antibacterial activity when silver ions are not eluted, or exhibit toxicity when silver ions are excessively eluted. Also, there may arise a problem that antibacterial activity cannot be maintained over a long period because the degree of elution of silver ions is unstable.